For certain boring operations it is necessary for the cutting tip to project not only radially over the circumference of the boring bar or over the outline of a toolholder fastened to the boring bar, but also in the axial direction. In addition, the cutting tip should be capable of fine adjustment in the radial direction. For this purpose it is known practice to mount, in a recess in the toolholder, a conventional tool insert in the housing of which is provided a cutting tip support capable of fine adjustment. The axis of this cylindrical recess is inclined at an angle of approximately 53.degree. relative to the axis of the boring bar, hereby fulfilling the requirement that the cutting tip should project forward over the toolholder in the axial direction of the boring bar. The inclined arrangement of the tool insert has the disadvantage that not only the desired radial adjustment of the cutting tip, but also the undesirable axial adjustment thereof take place whenever the cutting tip support is adjusted. Furthermore, the constructional dimensions, in particular the axial length of previously known tool inserts having fine adjustment of the cutting tip support, present certain difficulties for boring bars or tool supports often have central bores, for example for accomodating draw-in spindles to actuate cross slides, etc., or a centrally located screw which serves to fasten the toolholder to the boring bar. For this reason the tool insert cannot on any account extend beyond the centre of the toolholder, but must end even before the said centre in order that the fastening screw may extend past the rear end of the tool insert. A further disadvantage is the small range of adjustment of the tool inserts known for this purpose.
With another known tool insert intended particularly for boring bars, as described in the introduction (cp. German Pat. No. 1 752 012), the cutting tip support has a threaded pin at its rear end. This threaded pin is enclosed by a nut having a collar which is mounted free of play between two ball bearings in the housing of the tool insert, while being preloaded in the axial direction. An extension of the nut projects out of the rear end of the housing and, at this point, has a hexagonal head so that the nut can be turned. To prevent the cylindrical shank of the cutting tip support from being twisted relative to the housing, there is provided a transverse pin which engages in corresponding guide grooves extending in the axial direction of the shank. However, such a means of preventing twisting is only suitable when the effective cutting edge of the cutting tip is staggered only slightly relative to the shank axis. This known tool insert has a relatively great constructional length in the axial direction and is therefore unsuitable for the purpose described in the introduction when machining smaller diameters.
An insert having boring tools at both ends for transversely slotted boring bars is also known (cp. German Pat. No. 1 082 480), the said boring tools being adjustable with an adjusting spindle which is mounted in the longitudinal direction thereof and which has threads spaced at intervals and running in opposite directions. The adjusting spindle can be secured in the transverse hole by a transverse screw engaging in a slot. The adjusting spindle engages each female thread of the shank of the boring tool having a threaded pin, the front end of the said threaded pin having a hexagon socket which is accessible through an axial bore in the boring tool. This known insert cannot be used at all for the purpose mentioned in the introduction as the boring tools are only protected from torsional stress by a clamping screw.
The problem underlying the invention is to provide a tool insert of the type described in the introduction and for the purpose mentioned in the introduction, which has a short constructional length, has a relatively wide range of adjustment and can be fitted in a toolholder or in a boring bar in such a way that axial adjustment is prevented when the cutting tip support is adjusted in the radial direction. In addition, the tool insert should be characterised by stable mounting of the cutting tip.
This problem is solved in accordance with the invention in that
the front end of the housing comprises a transverse slot with bounding surfaces which extend substantially parallel to the plane of the cutting tip, PA0 that the front end of the shank has a cross piece, the lateral faces of which extend substantially parallel to the plane of the cutting tip and abut on the bounding surfaces of the transverse slot, PA0 that the recess for the cutting tip is provided at one end of the cross piece, which end extends at least as far as the wall of the housing, and PA0 that the thread in the shank is designed as a female thread, in which the adjusting element engages together, with a threaded pin, the front end of the said adjusting element having a hexagon socket which is accessible through an axial bore in the cross piece.
The new tool insert is characterised above all by its very short axial constructional length. It can therefore be inserted in the toolholder or in a boring bar in such a way that the axis of the cutting tip support extends perpendicular to the axis of the boring bar. Therefore, axial adjustment of the boring bar is always prevented whenever the cutting tip support is adjusted in the radial direction. Since the cutting tip is mounted on the cross piece mentioned, it projects in the axial direction over the toolholder or over the boring bar in the desired manner. In order to enable the considerable machining forces to be absorbed by this embodiment, the cross piece is mounted in a transverse slot, open at the front, in the housing and is supported by its lateral surfaces on the bounding surfaces of the transverse slot. A very stable and torsion-free mounting of the cutting tip support and therefore also of the cutting tip is hereby achieved. Moreover, it is advantageous that, with the tool insert according to the invention, the cutting tip support can be adjusted by the front side thereof. Owing to the play-free mounting of the adjusting element, the adjustments of the cutting tip support can be made with great precision.
Other advantageous embodiments of the invention are characterised in the sub-claims.